It has been suggested, for example in U.S. Pat. No. 2,480,085 dated Aug. 23, 1949 to George J. Mitchell, that a rotary ball mill be combined with a surrounding, concentric, co-rotating screen. In such apparatus, milled product containing solid particles above and below the product size specification can be delivered directly from the mill into the screen, and screened material can be recycled to the mill.
This general approach holds promise, at least theoretically, because such delivery and recycling can be performed without the necessity of using conveyors. Thus, substantial capital and operating cost savings as well as compact installations appear possible.
However, it is believed that there is a need to render the screen portions of such combinations more productive. It is known to employ vibratory devices to improve the productive capacity of some kinds of "stand-alone" screens, i.e. particularly those flat or curved but non-cylindrical screens that are not combined with mills. The purpose of the present invention is to provide rotary drum particle size reduction equipment combined with a co-rotating screen that at least partially surrounds the drum and that is readily susceptible to efficiency enhancement with vibratory exciters.